I have just acquired a Gary Russell 50mm Super Plossl to compare against my Tele Vue 55mm Plossl.
The GR50 has a Delrin body and a T2 thread on the eye lens end. A T2 to C connector from RAF Camera is used to make the connection with the NVD. Beautifully simple and easier to use than my TNVC adapter, so I hope the optics prove out.
Looking at the T2 connection, a thought occurred to me:
Could edge of field aberrations be reduced or eliminated using readily available T2 spacers to find an optimum spacing between eye lens and NVD objective lens?
Perhaps Tele Vue would have thought of that and dismissed the idea. Possible host eyepieces in the Tele Vue line-up are quite varied, yet the TNVC adapter has no provision for length (spacing) adjustment.
I think I will order some Baader T2 spacers from Agena Astro.